1. Field of the Invention
The present invention relates generally to very large scale integrated circuits and, more particularly, to microcircuit package assemblies.
2. Description of Relevant Art
In the manufacture of semiconductor devices the need for adhering a semiconductor chip, frequently referred to as a "die" to a suitable substrate, such as a metal or ceramic substrate, typically is satisfied by utilizing various types of adhesives, as a so-called "die attach". One type of adhesive which has been used is a silver/glass composition. Other adhesives typically utilized include gold/silicon eutectic formulations and epoxy compositions.
Such previously used adhesives have displayed certain decided disadvantages. For example, gold/silicon eutectics have been limited to die sizes less than about 5 millimeters square, primarily due to lack of process robustness. Epoxy adhesives, although offering some advantages in ease of processing, suffer from significant shortcomings in terms of thermal stability and adhesive strength under conditions of stress. Silver/glass adhesives, which comprise silver and glass particles dispersed in an organic vehicle, require precise temperature profiles to remove the organic vehicle at a controlled rate and to allow the residual silver and glass to bond the die to the substrate. They are suitable only for die sizes up to about 15 millimeters square. Moreover, silver/glass adhesives require curing at relatively high temperatures, in the neighborhood of 425.degree. to 450.degree. C., plus additional oven drying steps.
Recently, rapid curing polymeric adhesives incorporating a conductive filler have been introduced into the marketplace as an improvement over silver/glass adhesives. These adhesive materials are described in U.S. Pat. Nos. 5,150,195, 5,155,066, and 5,195,299 to My N. Nguyen. The adhesive formulations described therein are based upon cyanate esters which are liquid dicyanate monomers of the type described in U.S. Pat. No. 4,785,075 to David A. Shimp and U.S. Pat. No. 4,839,442 to Wallace M. Craig, Jr. The disclosures of these five patents are all, individually and collectively, incorporated herein by reference. The liquid dicyanate monomers are also described in an article entitled "New Liquid Dicyanate Monomer for Rapid Impregnation of Reinforced Fibers" by Shimp and Craig, Jr, presented at the 34th International Sampe Symposium in Reno, Nev., May 8-11, 1989.
The rapid curing adhesive formulations described in the Nguyen patents have been utilized extensively in the mass production of semiconductor devices sized from about 2 to 7 millimeters square. Semiconductor circuit manufacturing, however, increasingly is being directed toward higher integration and higher pin counts as well as specialized purpose semiconductor chips, for which larger dies, on the order of upwards of about 20 millimeters square, are required. Unfortunately, adhering larger sized dies to various substrates has previously resulted in relatively fragile microcircuit package assemblies.
It is accordingly an object of the present invention to provide a microcircuit package assembly in which the bond between the die and substrate is characterized by high thermal stability and excellent strength under conditions of stress.
Another object of this invention is to provide an improved large size ASIC type microcircuit package assembly.
Other objects and advantages of the present invention will become apparent in the course of the following detailed description and disclosure.